Abstract: A substrate for high-frequency circuits best suited as a substrate for a flat antenna to receive satellite-broadcast microwaves or as a similar substrate, the substrate comprising (i) a porous insulator layer wherein the proportion by volume of open cells to all the cells is at least 50% and (ii) a metal foil laminated over at least one side of the insulator layer through (iii) a water-impermeable film, and a process for making such substrates.

Abstract: A process for producing a fire retardant and heat resistant copper-clad laminated board, characterized in that a maleimide resin type varnish containing a small amount of a specific halogenated diphenyl ether compound is used for impregnation of base material therewith. Copper-clad laminated boards produced according to the present invention may be so improved in fire or flame retardant properties as to be classed 94 V-0 in accordance with UL 94 (vertical burning test), and, nevertheless, are not substantially downgraded in heat resisting properties as well as copper foil peel strength.

Abstract: A process for preparing a thermosetting maleimide type prepolymer which comprises reacting (A) a polyfunctional maleimide compound, (B) a bis-maleimide, (C) a diamine and (D) an epoxy compound. The maleimide type prepolymer prepared according to the process of the present invention has rapid curability and excellent solubility in low boiling point solvents such as acetone, methyl ethyl ketone and methyl cellosolve, which are available at low cost. Accordingly, the prepolymer is advantageously used especially for the production of laminated boards having good heat resisting properties, low moisture absorption and good adhesion to various substrates such as a copper foil.

Abstract: A process for preparing a thermosetting imide type prepolymer which comprises heating a bis-imide (A) and a diamine (B) in the presence of an organic solvent with a boiling point of 70.degree. to 170.degree. C. and heating the reaction mixture together with an epoxy compound (C). The imide type prepolymer prepared according to the process of the present invention has rapid curability and excellent solubility in low boiling point solvents such as acetone, methyl ethyl ketone and methyl cellosolve, which are available at low cost. Accordingly, the prepolymer is advantageously used especially for the production of laminated boards having good heat resisting properties, low moisture absorption and good adhesion to various substrates such as a copper foil.

Abstract: A process for preparing a thermosetting maleimide type prepolymer which comprises heating (A) a polyfunctional maleimide compound derived from a polyamine prepared from aniline and formalin, (B) a bis-maleimide and (C) a diamine. The thermosetting maleimide type prepolymer prepared according to the process of the present invention is excellent in solubility in low boiling point solvents such as acetone, methyl ethyl ketone and methyl cellosolve, which are available at low cost. Accordingly, the prepolymer is advantageously used especially for the production of laminated boards having excellent heat resisting properties.